CAMDEN, N.J. — The Boston Celtics and Philadelphia 76ers have agreed in principle to swap the Nos. 1 and 3 picks in Thursday’s NBA draft, and Philadelphia is expected to use the No. 1 pick on Washington guard Markelle Fultz, sources told The Undefeated’s Marc J. Spears, confirming news that was first reported by TNT’s David Aldridge.

The Celtics will receive at least one additional first-round pick in the deal, sources told ESPN. Sources say Philadelphia, on top of its No. 3 overall pick, is sending the 2018 first-round ‎pick it owns via the Los Angeles Lakers, which the Sixers acquired from Phoenix at the 2015 trade deadline.

But if that Lakers’ pick doesn’t fall between No. 2 and No. 5 in the 2018 draft, sources say, Philadelphia will instead send a 2019 first-rounder to Boston that it acquired from the Sacramento Kings.

The trade is likely to be finalized on Monday, sources said.

Fultz worked out for the 76ers on Saturday, a day after ESPN reported that the teams were in serious talks to swap their picks.

Fultz, donning a Philadelphia cap as he arrived at the team’s practice facility, visited the 76ers in a hastily arranged get-to-know-you session, with the workout and a meeting with team officials on his itinerary. His visit was expected to be one of the final hurdles to clear before Boston and Philadelphia could decide to actually consummate the trade.

“I let God take care of it,” he said. “I wake up every morning and get ready to go to the gym. I don’t really pay attention to everything that’s going on. I’m truly blessed to be in this position. Whatever happens, I’m looking forward to taking my talents to wherever I go.”

Once the trade is finalized, the first four spots in the draft order will exactly mirror the first-four order from last year: Philadelphia would have the No. 1 pick, the Lakers would choose No. 2, Boston would go No. 3 and Phoenix would select fourth.

Fultz’s rise to stardom has been rapid. In 2014, he was playing junior varsity basketball in high school. Barely three years later, he’s almost certainly going to become the NBA’s No. 1 pick. And if he gets to start his pro career by calling Philadelphia his new home, he’ll be living roughly a 2½-hour drive from his hometown of Upper Marlboro, Maryland.

“[The last few days have] been crazy, man,” Fultz said. “Just knowing that the draft is a couple days away, it’s been unbelievable. It’s been a blessing. Like I said, a dream I always had. I’m just anxious to get to that day and just get it over with so I can know where I’m going and put full investment into whatever team I’m going to.”

The 6-foot-4 guard averaged 23.2 points, 5.7 rebounds and 5.9 assists in 25 games during his lone college season at Washington, excelling on a team that finished 9-22 and lost its final 13 games. Fultz led the Pac-12 in scoring and finished No. 6 among all Division I players, and he was the top freshman scorer in the country.

Over the past 10 seasons, only two other freshmen had a better scoring average in college: Kevin Durant for Texas in 2006-07 and Michael Beasley for Kansas State in 2007-08.

Durant and Beasley were both No. 2 picks.

Fultz might be a few days away from going one spot better.

“I just wake up and go where they tell me to go,” Fultz said.

Philadelphia had the No. 1 draft spot on three previous occasions, taking Doug Collins in 1973, Allen Iverson in 1996 and Simmons a year ago.

With Simmons missing all of last season due to injury, the 76ers could be the first team to have two rookie No. 1 overall picks on the same team.

The 76ers have a top-three pick for the fourth straight year: No. 3 Embiid in 2014, No. 3 Jahlil Okafor in 2015 and Simmons in 2016. But with Fultz, Philadelphia — which has asked its fans to endure some very dismal stretches and “Trust The Process” for the past few years — would likely expect to turn a real corner toward respectability again.

Philadelphia went 28-54 this past season, after winning 19, 18 and 10 games in the previous three seasons.

Last season’s improved win total came with Okafor (50), Embiid (31) and Simmons (0) combining for 81 appearances, as Philadelphia’s trend of being absolutely snakebit by injuries continued.

However, Embiid and Dario Saric will finish in the top three when the NBA Rookie of the Year results are announced on June 26, and Simmons is expected to be ready for next season after recovering from foot surgery.